In tractors and similar heavy-duty vehicles, such endless tracks are drivingly supported by sprocket drums which are set in rotation via step-down transmissions whose housings are part of the drum supports. With the transmission housing largely surrounded by the drum, from which it is separated by an air space, the heat generated in the transmission can be dissipated only to a minor extent through the exposed drum surface and must therefore be carried off mainly by the vehicle frame which is itself subjected to no inconsiderable heating by the engine and associated components. In such vehicles, accordingly, cooling of the oil used to lubricate the lateral transmissions of their track mountings presents a problem.